A rate "lock" or "commitment" is a promise from the lender to hold a particular interest rate and a specific number of points for you for a specified period of time during your application process. This ensures that your interest rate can't go up during the application process.
While there might be a choice of rate lock periods (from 15 to 60 days), the extended ones are typically more expensive. You can get a longer period for your lock, but in choosing this option, will likely have a higher rate than you would have with a shorter span of time
In addition to choosing the shorter rate lock period, there are other ways you can get the lowest rate. A larger down payment will get you a reduced interest rate, since you're starting out with more equity. You could opt to pay points to bring down your rate for the term of the loan, meaning you pay more up front. For many people, this makes sense and is a good deal..
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